This invention relates to a position detector and, more particularly, to a position detector in which a movement of a permanent magnet is detected by a magnetic sensor element as a directional change in magnetic flux.
FIG. 4 illustrates a related position detector in sectional view. In this figures, the position detector comprises a magnetic sensor element 1 which includes a pair of magnetoresistance elements made of NiFe ferromagnetic magnetoresistive material formed in a magnetoresistive pattern on a glass substrate. The magnetoresistance elements are molded in a substantially rectangular insulating resin so that a magnetic sensing surface is formed by the magnetoresistance elements on the glass substrate surface.
Reference numeral 2 designates a position detector mold case made for example of a polybuthyleneterephthalate resin, 3 is a rotary shaft rotatably mounted to the case 2, 4 is an arm secured to one end of the rotary shaft.
Reference numeral 5 is a cylindrical permanent magnet secured to the other end of the rotary shaft 3, 6 is a ceramic substrate serving as a circuit board on which a sensor circuit including a wiring pattern and various electronic components are mounted, the magnetic sensor element 1 being mounted on the ceramic circuit board 6 with its magnetic sensing surface placed in parallel to the substrate surface. Reference numeral 7 designates a terminal for taking out an output from the magnetic sensor element 1, 8 is a cover of the resin case 2, 9 is an electromagnetic radiation shield box made of iron and surrounding the resin case 2, and 10 and 11 are washers.
As best seen from FIG. 4, the radiation shield box 9 is a relatively large box-shaped member made of iron with no bottom wall and surrounds substantially the entire outer surface of the case 2 and therefore the ceramic circuit board 6 on which the magnetic sensor circuit is mounted. The radiation shield box 9 is attached to the outer surface of the case 2 by means of screws or bonding agent (not shown). The radiation shield box 9 functions to shield and protect the electronic sensor circuit on the circuit board 6 against the external electromagnetic radiation.
The ceramic circuit board 6 is inserted within the case 2 with its board surface perpendicular to the permanent magnet 5, that is, with the magnetic field from the permanent magnet 5 parallel with the magnetic sensing surface of the magnetic sensor element 1.
When the position detector is applied to a throttle valve (not shown) of an internal combustion engine (not shown), the arm 4 is rotated in accordance with the opening degree of the throttle valve within an air-intake pipe of a vehicular engine, the rotation of the arm 4 is transmitted to the permanent magnet 5 through the rotary shaft 3. As the permanent magnet 5 rotates, the direction of magnetic flux passing in parallel across the magnetic sensing surface of the magnetic sensor element 1 changes, in accordance with which the resistance of the magnetoresistance pattern of the magnetoresistance elements changes.
With the above-described structure of the related position detector, the radiation shield box 9 must be externally attached to the detector case 2 by a suitable securing means such as screws and bonding agent, so that the manufacturing efficiency is not satisfactorily high. Also since the radiation shield box 9 must encase a substantial portion of the detector case, it is inevitably relatively large and heavy. Also, since the shield box 9 constitutes the outer surface of the position detector, the external appearance of the detector is apt to degrade, particularly after long-term usage.